Wideband self mixing millimeter wave receiver

ABSTRACT

A self-mixing antenna-mixer millimeter wave receiver has the local oscillator and the mixer combined in one single unit, using a Gunn diode (or other device) placed at the center of a spiral antenna and proper voltage applied, so that the diode becomes an oscillator. At the same time the diode will function as a mixer for the input signals received by the spiral antenna. The IF frequency from the mixer can be amplified and detected for further processing. Only a dc power supply is required to feed the diode at the center of the antenna.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmentaI purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

The present invention relates generally to a wideband self mixingmillimeter (MM) wave receiver, and more particularly to a receivercombined with a spiral type antenna.

To provide wide band coverage at mm wave frequencies, antenna detectors(antector) and antenna mixers have been pioneered by several engineers.The basic approach of an antenna detector is to use a diode detectormounted at the center of a spiral antenna, which covers a wide frequencyrange. This kind of receiver is very small in size, but the sensitivityof the receiver is low, typically -30 to -40 dBm. The antenna mixerapproach uses a mixer at the center of the spiral antenna. The output ofthe receiver will be at an intermediate frequency (IF) where anamplifier can be added to improve the sensitivity. Although thisapproach can improve the sensitivity of the receiver, it also increasesthe size of the receiver because a local oscillator is needed.

U.S. Patents of interest include U.S. Pat. No. 4,287,603 to Moser, whichdiscloses a radiated input mixer for converting a radio frequency signalto an intermediate frequency signal with the aid of a local oscillatorsignal. U.S. Pat. No. 4,319,248 to Flam discloses an integrated detectordevice sensitive over a broad band of frequencies. U.S. Pat. No.3,246,245 to Turner and U.S. Pat. No. 3,296,536 to Copeland et al eachdisclose a combined spiral antenna and converter circuit. U.S. Pat. No.4,368,472 to Ghandi discloses a dosimeter which includes a spiralantenna and a schottky diode. U.S. Pat. No. 3,509,465 to Andre et aldiscloses a spiral antenna having an amplifier and bias feed circuitsintegrated therein. U.S. Pat. No 3,949,407 to Jagdmann et al discloses adirect fed spiral antenna element array.

SUMMARY OF THE INVENTION

An objective of the invention is to provide a millimeter wave receiverhaving small size and high sensitivity.

A self-mixing antenna-mixer millimeter wave receiver according to theinvention has the local oscillator and the mixer combined in one singleunit, for example, using a Gunn diode placed at the center of a spiralantenna and proper voltage applied, so that the diode becomes anoscillator. At the same time the diode will function as a mixer for theinput signals received by the spiral antenna. The IF frequency from themixer can be amplified and detected for further processing. Only a dcpower supply is required to feed the diode at the center of the antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic and functional block diagram of a prior art basicantenna-detector (antector) circuit;

FIG. 2 is a schematic and functional block diagram of a prior art basicantenna-mixer circuit; and

FIG. 3 is a schematic and fuctional block diagram of a basic self-mixingantenna-mixer millimeter wave receiver circuit.

DETAILED DESCRIPTION I. Antenna Detector (Antector)

As shown in FIG. 1, a typical prior art antenna-detector type circuituses a diode detector 10 mounted at the center of a spiral antenna 12.The spiral antenna covers a wide frequency range, typically severaloctaves. The diode 10 is mounted at the two inner terminals (typicallythe feed point) of the spiral antenna 12. One outer terminal 14 of theantenna is connected to ground. The other outer terminal 16 of theantenna is connected to the input of a video amplifier 18. The inputsignal is detected by the detector 10 and converted to a video signal.The video amplifier 18 will amplify this signal for further processing.This arrangement forms a wide band crystal video receiver with asensitivity of -30 to -40 dBm. Because RF amplifiers covering a widefrequency range are not available, the sensitivity of this receiver isdetermined by the performance of the detector and the video amplifier.This type of receiver has the advantage of low cost and small size whichare critical for many applications, such as in tactical aircraft.

II. Antenna Mixer

In order to significantly improve the sensitivity of the antectorreceiver of FIG. 1, amplification must be provided before the detector.The center diode 20 can be used as a mixer rather than a detector, asshown in FIG. 2. A local oscillator 21 (LO) must be added, and theoutput of the local oscillator is applied to the diode mixer 20. Theinput signal will mix with the local oscillator frequency and bedownconverted to an intermediate frequency (IF). If the IF is kept under20 GHz, a conventional amplifier 25 can be used to amplify the outputbefore the detector 26 to improve the sensitivity of the receiver. Thereare many approaches for coupling LO power into the mixer diode, such asfeed through fin lines, suspended striplines, and through a cavityresonator. The additional local oscillators and feed network requiredincrease the complexity of the receiver design. There are also manyapproaches for coupling the IF signal out of the mixer.

III. Self-Mixing Antenna Mixer Scheme

Although the antenna mixer approach of FIG. 2 can improve thesensitivity of the millimeter (MM) wave receiver as compared with theantenna detector scheme of FIG. 1, the antenna mixer is more complicatedin structure. Adding a local oscillator and the necessary feedingcircuits will certainly increase the size of the receiver. In the novelself-mixing antenna mixer circuit shown in basic form FIG. 3, the localoscillator and the mixer will be combined in one single unit. Forexample, if a Gunn diode 30 is placed at the center of a spiral antennaand proper voltage is applied from a direct-current supply 31, the diode30 will become an oscillator. At the same time, the diode 30 willfunction as a mixer for the input signals received by the spiral antenna32. The IF frequency from the mixer can be amplified and detected forfurther processing. There are many different ways for coupling the IFsignal out of the mixer.

One typical form for the antenna 32 comprises spiral strip lines with aground plane on a printed circuit type board. The direct current canthen be fed via conductors extending through holes through the groundplane and the board.

The approach shown in FIG. 3 will eliminate the local oscillator unit ofFIG. 2 and all of the RF circuit required to couple the local oscillatorto the mixer at the center of the antenna. Only a dc power supply isrequired to feed the diode in the center of the antenna. The size of theself-mixing approach can be potentially very small due to thesimplification of the design, and at the same time maintains the highsensitivity.

It is understood that certain modifications to the invention asdescribed may be made, as might occur to one with skill in the field ofthe invention, within the scope of the appended claims. For example,other type diodes, or devices having more than two terminals, might beused in place of the Gunn diode. Therefore, all embodiments contemplatedhereunder which achieve the objects of the present invention have notbeen shown in complete detail. Other embodiments may be developedwithout departing from the scope of the appended claims.

What is claimed is:
 1. A self-mixing antenna-mixer millimeter wavereceiver having a local oscillator and a mixer combined in a singleunit, comprising a spiral antenna having two arms, each having an innerend and an outer end, a Gunn diode having two terminals connecteddirectly to the inner ends of the two arms at the center of the spiralantenna, means for coupling a source of direct current to the twoterminals of said diode via leads used only for the direct current andconnected directly to the inner ends of the two arms at the center ofthe spiral antenna, so that the diode becomes an oscillator, and at thesame time the diode functions as a mixer for input signals received bythe spiral antenna.
 2. A receiver according to claim 1, wherein theouter end of one of the arms of the spiral antenna is connected toground, and the outer end of the other arm is coupled to an IFamplifier, a detector, and a video amplifier in tandem, so that an IFfrequency from the mixer can be amplified and detected for furtherprocessing.
 3. A self-mixing antenna-mixer millimeter wave receiverhaving a local oscillator and a mixer combined in a single unit,comprising a spiral antenna having two arms, each having an inner endand an outer end, a semiconductor device having at least two terminalsconnected directly to the inner ends of the two arms at the center ofthe spiral antenna, means for coupling a source of direct current tosaid device via leads used only for the direct current and connecteddirectly to the inner ends of the two arms at the center of the spiralantenna, so that the device becomes an oscillator, and at the same timethe device functions as a mixer for input signals received by the spiralantenna.
 4. A receiver according to claim 3, wherein said semiconductordevice is a Gunn diode.